Regenerative paint drying system for continuous strip



April 8, 1969 3,437,321

REGENERATIVE PAINT DRYING SYSTEM FOR con'rmuous STRIP D. M. WILKINSONSheet Filed May 26, 1967 INVENTOR DW/GHZ' M WILKINSON ATTQRNEXW April 8,1969 o. M. WILKINSON ,3

REGENERATIVE PAINT DRYING SYSTEM FOR CONTINUOUS STRIP Filed may 26, 1967Sheet 8 of 4 FIG. 2

INVENTOR DWIGHT M. WILKINSON ATTORNEY April 8, 1969 o. M. WILKINSON3,437,321

REGENERATIVE PAINT DRYING SYSTEM FOR CONTINUOUS STRIP Filed lay 26, 1967Sheet 3 of 4 SIGNAL GENERATOR s| v 5e POWER SUPPLY FIG. 4

v INVENTOR DWIGHT M WILKINSON ATTORNEY April 8, 1969 n. M. WILKINSONREGENERATIVE PAINT DRYING SYSTEM FOR CONTINUOUS STRIP Sheet Filed lay26, 1967 INVENTOR DWIGHT M. WILKINSON ATiTORMEZ.

United States Patent US. Cl. 263-3 8 Claims ABSTRACT OF THE DISCLOSUREThis specification discloses a paint drying system in which the vapoursof the volatile solvents are burned to eliminate pollution of theatmosphere and the heat generated by such combustion is employed topreheat the incoming fresh air thereby reducing the fuel required to drythe paint.

This invention relates to apparatus for drying and baking paint on acontinuous painting line.

The continuous painting or coating of strip material such as sheet metalrequires the use of high efliciency continuous oven dryers which applyheat in various stages to evaporate the volatile solvents and to bakethe paint. In the normal case the paint used contains considerablequantities of volatile solvents which are evaporated in large quantitiesand constitute a serious disposal problem.

In the past, it has been common practice to vent these volatile solventsdirectly into the atmosphere. As a result, municipal regulations havebeen adopted in certain areas prohibiting the dumping of these solventefi'luents which otherwise constituted a serious source of airpollution. Operators of such coating plants have therefore been forcedto adopt some system for the removal of the volatile eflluents down to apredetermined maximum level. Unlike sooty carbon deposits, volatileefiluents are difiicult to filter, and, although they may be recoveredby a distillation or condensation process, the equipment required forsuch processes is costly to manufacture and difficult to install inexisting plants and may be subject to variations in the efiiciency ofeifiuent extraction due for example to different concentrations ofeffluents encountered in the waste air stream.

An alternative method of efiluent removal is simply to oxidize theeffluents by burning them in the waste air stream. Such oxidization isagain subject to variations due to variations in the eflluent content ofthe waste air system and although the equipment required is very muchcheaper than the distillation or condensation equipment referred toabove, there is no efiluent recovery to offset such cost and the processbecomes increasingly wasteful.

Accordingly, it is an objective of the present invention to provide apaint drying and baking system incorporating high efiiciency ovens foreffective and rapid drying and baking of the paint on a continuouslymoving strip and further incorporating effluent oxidizing means which isregenerative in nature and assists in maintaining the efiiciency of theovens.

More particularly, it is an objective of the present invention toprovide a system having the foregoing advantages in which the ovens areautomatically self-regulating to maintain a constant temperature levelat the surface of the metal strip with a minimum of temperaturefluctuations.

3,437,321 Patented Apr. 8, 1969 adjustable over a wide range to insuresubstantially complete oxidizing of the volatile eflluent constituent ofthe waste air stream at all levels of concentration encountered.

More particularly, it is an objective of the present invention toprovide a system having the foregoing advantages in which the heatgenerated by oxidizing of the volatile efiluents is employed forpreheating the incoming air stream prior to entry into the oven systemthereby conserving the overall energy required for drying and baking thepaint and minimizing the losses due to waste of volatile solvents.

The foregoing and other advantages will become apparent from thefollowing description of a preferred embodiment of the invention whichis given here by way of example only, with reference to the followingdrawings in which like reference devices referred to like parts thereofthroughout the various views and diagrams and in which;

FIGURE 1 is a schematic block diagram showing the overall system ofovens, oxidizing means, and heat exchange system;

FIGURE 2 is a sectional side elevational view of a typical oven as usedin the system of FIGURE 1 showing alternative positions of memberstherein in phantom form;

FIGURE 3 is a plan view partially cut away and sectioned of a portion ofone of the burners of the oven of FIGURE 2;

FIGURE 4 is a schematic block diagram showing the operation of controlsystem of the oven of FIGURE 2;

FIGURE 5 is a sectional side elevation of an efiiuent burner used foroxidizing the volatile efiluents in the system of FIGURE 1;

FIGURE 6 is greatly enlarged sectional side elevation of a portion of aburner element as shown in FIGURE 5;

FIGURE 7 is a sectional side elevational view of an alternative form ofeffluent burner; and

FIGURE 8 is a schematic view of a further embodiment of efiluent burner.

Referring to FIGURE 1 the apparatus shown comprises a Number 1 HeaterOven 11, Number 2 Heater Oven 12, and Number 3 Heater Oven 13. Material,which in this case is strip metal 14 is fed through the ovens in orderto exit as at 15 with the paint dried. It should be understood that theapparatus shown in FIGURE 1 is an intermediate portion of a completepainting line and that in operation the various types of cleaning andspraying operations would take place prior to the entrance of the stripas at 14 and cooling and other finishing operations as maybe requiredwould take place after the strip leaves as at 15, the drying apparatusshown in the figure.

Each of the drying ovens is quite similar in construction and isprovided with a heating unit 16, 17 and 18 respectively, the ovens inthis case being gas fired. Details of construction for such gas firedovens are described below with reference to FIGURES 2, 3, and 4.

The apparatus shown in FIGURE 1 is utilized for drying paint containingvolatiles and does so by a pre-heating and partial drying by means ofthe oven 11, a second heating by means of the oven 12 in which theremainder of any of the heavier volatiles are driven from the paint, anda final drying or baking process by means of the oven 13.

The air intake to oven 11 is pre-heated by means described below for theprimary evaporation and it is then preferable to transfer the heated airfrom oven 11 to oven 12 by means of the pump 19 operating through thepipes 20 and 21. By utilizing the heated air from oven 11 introducedinto oven 12 where additional heat is supplied by means of heater 17economy of operation with regard to fuel input is improved. The efiluentfrom the drying of paint entrained with waste air exist through thepiping at 22 and driven by the fan unit 23 is forced through a burnerunit 24.

The burner unit 24 utilizes a variable fuel input through the intake 25and by raising the heat of the effluent from the fan 23 oxidizes thesolvents contained therein.

The considerable amount of heat generated, both from the burning of thefuel input from 25 and from the solvents from the effluent from thedrying process, is utilized by means of heat exchanger 26 heating theincoming air as at 27 utilized in the entire drying process. Waste gasesand oxidized effiuent exit at 28, the burner effectively reducing thepercentage content of solvents to acceptable limits.

The burner unit 24 employed in the present invention is described belowwith reference to FIGURES 5, 6, 7 and 8.

A fan unit 29 is used to force the incoming pre-heated air fromexchanger 26 into the first oven 11. In some cases it may be necessaryto provide an additional heat input by means of the heater 30 suppliedby the line 31 with fuel should the heat available from the heatexchanger 26 not prove suflicient for particular installations. Theheater 30 can be gas fired similar to the ovens 11, 12 or 13 or ifdesired other means of heating the air introduced into oven 11 can beresorted to.

With reference to FIGURE 2 an oven such as 11 is utilized for drying apainted strip shown and indicated generally as 14, adapted for movingthrough the oven, having paint on both sides which is dried during thepassage therethrough. A plurality of upper burner assemblies at 32 and aplurality of lower burner assemblies at 33 are pivotally supportedwithin the oven and operably connected to respective operating pistons34 and 35 of any suitable type.

The radiating burners such as burners 36 or 37 can be of any suitabletype and can for instance be gas fired infrared burners such as the typeemploying surface combustion phenomena to produce the heat radiation.Each individual burner is pivotally supported within the oven and isinterconnected by means of linkages, such as linkages 38 and 39 in orderto be operable in unison with the respective operating cylinder. Theoperable position is as shown in solid line and the inoperable ornon-heating position is as shown in the chain dotted line as at 40 and41. It should be noted that if desired other arrangements of infraredheating units can be resorted to, the arrangements shown in the drawingbeing done so by way of example only.

The air intake and outlet for oven have not been shown in thisillustration for the sake of clarity, since the construction of theovens 16, 17 and 18 will be essentially similar. However, while inFIGURE 1 there has been shown an arrangement of ovens 16 and 17connected for seires flow of air from one to the other, it will readilybe understood that other connections might be arranged such as aconnection in parallel whereby each oven received fresh preheated airfrom fan 29 and delivered solventsaturated effluent separately to fan23.

Referring to FIGURE 3 a preferred method of mounting an individualinfrared burner which in this case is a gas rfired infrared burner, isshown. The oven wall 42 supports in bearing 43 a hollow shaft 44connected through fitting 45 to the infrared burner 46. A simpletrunnion mount is utilized at the extreme other end of the burner 46this not being shown in the drawing.

A slip joint assembly 47 is sealably secured to end 48 of the shaft 44and is sealed gas tight by means of the seal 49 and to be retained bypin 50 engaged within the annular slot 51. A gas valve 52 is supplied inthe gas supply line 53 supplying fuel to the burner 46.

Referring to FIGURE 4 a schematic of the device is shown whereincylinders 34 and 35 are hydraulic and are supplied selectively from thethree ways valve 54 which receives hydraulic power through the lines 55.The selective position of valve 54 is controlled by means of the switchunit as at 56 having an opened position thus to give the two positionsfor operation of valve 54 and the respective extended or retractedposition of the cylinders 34 and 35. Control of the valve 54 from switch56 is eifected from the main control source of the painting line wherebyupon the line being stopped the burners 36 and 37 are moved to theinoperative position and upon the line being started the burners aremoved to the operative position as described above.

The gas burners 36 and 37 are controlled by means of the turn down valve57 which in turn is responsive to the sensor 58. This sensor ispositioned adjacent to the work as it leaves the furnace as shown inFIGURE 2 and senses the heat radiated from the work and thus is anindication of the temperature of the work leaving the oven. Suitablesignal conditioning means in the form of amplifier 59 and variablesignal output 60 supplied by power supply 61 provide a signal for thevalve 57 in order to regulate the fuel supply to the burners from supplyline 62.

In use the work 14 can be fed through the oven and during normal passageof the work therethrough the burners are in a position to radiate heatonto the work and thus to dry the paint. Upon stoppage of the line, oreven a major slow down in the line, the switch means 56 will throughvalve 54 cause the cylinders 34 and 35 to actuate and move the radiantburners away from the work.

In order to control the temperature at which the work leaves the oven,the sensor 58, responsive to radiation from the work 14 provides avariable signal to the amplifier and output system thus to vary thesupply of fuel to burners 36 and 37.

An additional sensor (not shown) is preferably located within each ovenwhich senses the ambient (air) temperature, which is a function of theheat of incoming air and additional heat of the gas burners, and isconnected in the same way as sensor 58 to control the supply of fuel tothe burners. Thus, even where the line is temporarily halted, the fuelsupply to the gas burners will be controlled notwithstanding that sensor58 is rendered temporarily useless.

Thus by utilizing the gas valve 57 controlled by means of the sensor 58,the heat supplied to the work piece as it moves through the drying ovencan be controlled.

Additionally should it become necessary to control the heat within theoven during which times the radiant burners are not directed at thework, vent means such as for instance the controllable vent 63 as shownin FIGURE 2 can be utilized. In most cases the heat resulting fromconvection off the burners will be considerably below that resultingfrom radiation and normal heat loss through the walls of the oven willbe sufficient to maintain a low temperature therewithin. However, insome cases where the heat loss is not sutficient or where the input dueto the burners is excessive, venting means such as described may beresorted to.

The volatile effluent burner system shown in FIG- URES 5 and 6 will beseen to be located in the effiuent flow duct at 24 and according to thispreferred embodiment of the invention it is provided with a gas flowbarrier comprising, in this preferred embodiment at least two flatpanels 64 formed of porous ceramic material. Panels 64 are supported ina generally V-shaped orientation within the duct at 24 by resilientsupport means 65 fastened to the side walls of the duct and resilientsupport means 66 fastened across the side walls of the duct andsupported at intervals as by supporting bar 67. Burner means areprovided in the form of gas burners 68 supplied with fuel through thepiping system 69. The burners 68 are positioned at the upstream end ofthe panels 64 the flame thereof being directed along the inside surfaceas at 70.

With particular reference to FIGURE 6 the action of the flame 70 panels64 is shown diagrammatically. The hot gases and flames from the burners68 are indicated at 70 and the waste air laden with volatilehydrocarbons is indicated at 71. The porous ceramic material of panels64 allows passage of the hot products of combustion from the flame andthe waste gas 71 therethrough and causes instant mixing of the waste gaswith the hot flame so as to ensure oxidization of the volatile solvents.The eflluent gas indicated at 72 on the downstream side of the panels 64is thus a mixture of both the flame gas and the waste gas in which thesolvents have been burnt.

With reference to FIGURE 7 a further configuration for a barrier membersuch as for instance the panel 73 is shown placed within a gas duct 74and has a pair of burners 75 and 76 directing flames therefrom along theupstream side of the barrier 73. Thus for a simple application a singlebarrier member together with one or more gas flame burners can beutilized to effectively oxidize any solvents existing in the waste gasfrom a drying process. While a single barrier 73 is shown in FIGURE 7and a pair of barriers 64 are shown in FIGURE 5 it should be understoodthat such arrangements can be used in plurality within a particular ductin order to increase the effective capacity of the installation.

With reference to FIGURE 8 such a system employing a plurality ofbarriers is shown wherein the barrier members as indicated at 77 aremounted within a large duct 78 and are provided with a plurality ofburners as at 79. The waste gas containing volatile solvents isintroduced at 80 and passing through the barriers 77 where the solventsoxidize and exit at 81. Thus for particularly large installations acertain size of overall area of barrier and burner unit can be used inplurality to effect complete handling of the full capacity of the ductsystem. It should also be noted that the plurality arrangement as shownin FIGURE 8 can be varied according to individual requirements for spaceand design conditions. Other configurations will occur to those skilledin the art to suit particular installations and the configurations shownare done so by way of example only.

As an example of a typical installation for oxidizing air laden withvolatile solvents from a paint drying process the following conditionsand dimensions for a burner are given. For a duct height ofapproximately twelve inches and of a width suitable to handle therequired air flow the configuration as shown in FIGURE 5 can be used toadvantage. Each burner should have a rating of approximately 350,000B.t.u. per hour per lineal foot of burner to provide a sufiiciently hotgas blanket over the length of the barrier members. It is preferred toform the barriers out of a one-inch thick plate of silicon carbideporous media having a grade of 210 as specified by the CarborundumCompany, Bond Abrasive Division, PO. Box 37, Niagara Falls, NY. Thiswould handle an air flow of approximately 210 cubic feet per minute overeach square foot of barrier media at a two inch W.C. pressure dropthrough the barrier. The fuel would be natural gas.

The temperature of the combustion gases from the burners required forefficient oxidization of the solvents will vary between 900 F. and 1350F. To some extent this may depend also upon the residence time duringwhich the solvent vapours remain in contact with the hot combustiongases, the object being to achieve the highest rate of oxidisation withthe shortest possible residence time. The intimate mixing of the solventvapours and the combustion gases greatly increases the efliciency andthis mixing is significantly improved by the use of porous barriers suchas those described above. In some instances aluminum oxide porousbarriers may be acceptable although at reduced temperatures.

In some instances it may be desirable to regulate the pressure dropthrough the system in order to effectively control complete oxidizationof the solvents contained in waste gas. In such a case an adjustableorifice as indicated generally at 82 in FIGURE 5 can be resorted to. Theorifice as shown in FIGURE 5 comprises a pair of plates 83 and 84slidably mounted within the mounting 85 and moveably responsive to asuitable transducer to effectively close or open the opening indicatedat 86 to throttle the air stream moving therethrough. Thus while controlof the burner flame, by using available equipment, will control thetemperature at which the Waste gas comes in contact with the flame, theadjustable orifice, provided with suitable automatic controlinterconnected with the transducer, will control the pressure dropthrough the porous media and thus control the time of contact of thesolvent volatiles with the hot gas flame thus to control the degree ofoxidization of these volatiles.

Other means for the control of pressure drop within the duct and thusthe time of contact of the hot gas flame and the solvents can beresorted to, the means shown in the drawings being done by way ofexample. Thus many well-known types of dampers can be employed withinthe duct system either upstream or downstream of the efiluent burnerunit to control the pressure drop within the complete unit. Essentiallyany means tending to constrict the area of air passage through thedevice will affect the pressure drop through the system and control ofthis means will control the pressure drop and the time of contact.

From the foregoing it will be seen that the present invention providesmeans for effectively oxidizing volatile hydrocarbons in a gas stream.The invention provides for variation in temperatures at which thehydrocarbons are oxidized and also provides for variation in time ofcontact of the hydrocarbons with the high temperature regions thus toeffectively oxidize the hydrocarbons to the desired degree.

What I claim is:

1. Regenerative paint drying system for use in association with acontinuous strip painting line and comprising: heating oven meansincluding at least two heating ovens adapted to enclose at portion ofsaid continuous strip spaced apart along said strip and evaporatesolvents from paint thereon; variable strip heating means within eachsaid oven; intake and exhaust conduit means for conducting air to partof said oven means, and for conducting solvent-laden efliuent airtherefrom; solvent burning means in said exhaust conduit means foroxidizing solvent vapours in said eflluent; heat exchange means inthermal communication with the eifluent emerging from said solventburning means for pre-heating intake air entering said intake conduitmeans; and heat regulating means sensing the temperature in the firstsaid oven resulting from the combined effect of said strip heating meansand said heated intake air and varying the heat input of the second saidoven strip heating means.

2. Regenerative paint drying system as claimed in claim 1 includingfurther heat exchange means associated with said intake conduit meansoperable to further preheat said air flowing therein.

3. Regenerative paint drying system as claimed in claim 1 wherein saidvariable oven heating means includes radiant burner means fired by gasfuel, said burner means being pivotally mounted within each said ovenfor movement between an operating position in which the radiant heat isdirected towards said continuous strip and a non operating position inwhich the radiant heat is directed away from the continuous strip, andmeans for moving said burner members between said two positions.

4. Regenerative paint drying system as claimed in claim 3 includingambient temperature sensing means within said oven means, and means forsensing the temperature of said continuous strip, said sensing meansproviding a control signal, and gas flow valve means responsive to saidcontrol signal to regulate the flow of gas to said burner means.

5. Regenerative paint drying system as claimed in claim 1 wherein saidsolvent burning means includes a burner chamber; a porous barrier withinsaid burner chamber formed of high temperature resistant material andproviding a predetermined cross sectional area for flow of effluenttherethrough; and fuel burner means on the upstream side of said barriermember providing combustion gases at a predetermined temperature, saidcombustion gases and said eflluent being intimately mixed one with theother in passage through said porous barrier means.

6. Regenerative paint drying system as claimed in claim 1 including gasfiow regulating means in said exraust conduit means operable to regulatethe flow of effluent therethrough.

7. Regenerative paint drying system as claimed in claim 1 wherein saidsolvent burning means includes at least one porous barrier member ofhigh temperature resistant material of fiat planar construction arrangeddiagonally relative to the flow axis of effluent within said conduitmeans whereby to define a continuously decreasing flow area on theupstream side of said conduit means and a continuously increasing flowarea on the downstream side of said conduit means, and including fuelburner means on the upstream side of said barrier means located closelyadjacent thereto at about the point of maximum flow area and oriented todirect combustion gases along the upstream surface of said barriermember towards the point of minimum flow area.

8. Regenerative paint drying system as claimed in claim 1 wherein saidsolvent burning means includes at least two porous barrier members offlat planar construction located within said exhaust conduit andarranged in a V-shaped configuration the apex of said V being orientedtowards the downsream portion of said conduit, and fuel burner meansarranged adjacent the barrier members at the widest portion of saidV-shape on the upstream side thereof.

References Cited UNITED STATES PATENTS 2,658,742 11/1953 Suter et al2633 2,804,694 9/1957 Clipsham 2633 3,106,386 10/1963 Harris 26333,183,605 5/1965 Argue et a1. 2633 X JOHN J. CAMBY, Primary Examiner.

U.S. Cl. X.R.

